Laval University Cancer Research Centre, Hôtel-Dieu de Québec (CHUQ), Quebec City, Québec G1R 2J6, Canada.
Nucleic Acids Res. 2012 Nov 1;40(20):10452-62. doi: 10.1093/nar/gks748. Epub 2012 Aug 16.
Among the set of Argonautes proteins encoded by metazoan genomes, some have conserved amino acids important for catalytic or slicing activity. The functional significance of these residues in microRNA (miRNA)-specific Argonautes in animals is still unclear since miRNAs do not induce site-specific cleavage of targeted messenger RNAs (mRNAs), unlike small interfering RNAs (siRNAs). Here, we report that miRNA-specific ALG-1 and ALG-2 Argonautes from Caenorhabditis elegans possess the slicing activity normally implicated in the siRNA-silencing pathway. We also find that ALG-1/2 can bind and use a Dicer-processed miRNA duplex to target mRNAs, suggesting an ability to displace RNA strands. Importantly, the slicing activity of ALG-1 or ALG-2 is essential for the miRNA pathway in vivo, as shown by the accumulation of truncated miRNA precursors and altered miRNA-induced silencing complex (miRISC) formation. Taken together, our data demonstrate that the slicing activity of Argonautes contributes to a new and unexpected step in the canonical miRNA pathway that occurs prior to miRISC loading in animals.
在后生动物基因组编码的 Argonautes 蛋白组中，有一些具有对催化或切割活性很重要的保守氨基酸。这些残基在动物中 miRNA（microRNA）特异性 Argonautes 中的功能意义尚不清楚，因为 miRNA 不像小干扰 RNA（siRNA）那样诱导靶向信使 RNA（mRNA）的特异性切割。在这里，我们报告线虫的 miRNA 特异性 ALG-1 和 ALG-2 Argonautes 具有通常与 siRNA 沉默途径相关的切割活性。我们还发现，ALG-1/2 可以结合并利用 Dicer 处理的 miRNA 双链体来靶向 mRNAs，这表明其具有置换 RNA 链的能力。重要的是，ALG-1 或 ALG-2 的切割活性对于体内的 miRNA 途径是必不可少的，这表现在截断的 miRNA 前体的积累和 miRNA 诱导的沉默复合物（miRISC）形成的改变。总之，我们的数据表明 Argonautes 的切割活性有助于动物中 miRISC 加载之前的经典 miRNA 途径的一个新的和意外的步骤。
